Peripheral neuropathy is one of the major complications of diabetes. There is a compelling need to develop effective therapeutic approaches specifically designed to improve neurological function in the damaged peripheral nervous system after diabetes. Thymosin 4 (T4), a major intracellular G-actin- sequestering peptide, has multiple biological functions, including promotion of remodeling of injured and damaged tissues, and increasing angiogenesis after myocardial infarction. However, the role of T4 in diabetic peripheral neuropathy has not been investigated. In a novel set of experiments, our data show that Tbeta4 remarkably improved sciatic nerve vascular function and peripheral nerve function in diabetic mice, indicating that T4 may have a beneficial effect on the clinical treatment of diabetic peripheral neuropathy. In this application, we therefore seek to investigate the mechanisms underlying the therapeutic effects of T4 on the treatment of diabetic peripheral neuropathy. We propose that T4 by improving vascular function ameliorates diabetic peripheral neuropathy. Our hypotheses are: 1. Treatment with Tbeta4 improves neurological function of peripheral neuropathy in diabetic mice. 2. The Ang/Tie2 signaling pathway mediates the therapeutic effect of T4 on neurovascular function in diabetic peripheral neuropathy. 3. The PI3K/Akt signaling pathway underlies the effect of Tbeta4 on Ang1/Ang2 expression. To investigate the effect of T4 on neurological outcome, type II diabetic mice which develop severe peripheral neuropathy will be treated with T4 at various time points after onset of diabetes. To investigate the molecular mechanisms that mediate Tbeta4-enhanced neurovascular function in diabetic mice, the effect of T4 on expression of Ang/Tie2 and activation of PI3K/Akt signaling pathway will be examined. Using pharmacological inhibitors and siRNA gene knockdown techniques, we will investigate the cause-effect of the Ang/Tie2 and PI3K/Akt signaling pathways on regulating T4-enhanced neurovascular function and axonal outgrowth. These studies are innovative and will provide new insight into mechanisms underlying the neurological dysfunction of diabetic peripheral neuropathy and lead to the development of a new treatment using T4. Relevance Statement: Peripheral neuropathy often stemming from diabetes is a major disability affecting millions of Americans. In this proposal, employing preclinical studies in the diabetic animal, I seek to develop a novel treatment for peripheral neuropath using T4. T4 is currently in a phase II clinic trial for the treatment of patients with acute myocardial infarction. In this proposal, I also elucidate the molecular mechanism by which T4 is therapeutically effective. This research will provide the essential pre-clinical data for translation to a phase 1 clinical trial.